Santonox, 4,4'-thio-bis(6-tert-butyl-m-cresol), has been recommended for study in the NTP as a representative of the class of rubber antioxidants which have widespread industrial usage and a high potential for occupational exposure. Santonox is relatively non-toxic, with an oral LD50 of approximately 5g/kg. Before being tested in the bioassay program, disposition studies are needed to assess its absorption, distribution, metabolism, and excretion. Such studies will not only result in more appropriate dose settings, but a better understanding of the mechanism of toxicity of this class of compounds.